Wireless communication apparatus, communication method, and communication system

ABSTRACT

A decrease in access rate to a wireless medium caused by an exposed terminal apparatus is improved. A wireless communication apparatus of the present invention includes a reception unit that receives a frame indicating start of a medium protection operation, and acquires, from the frame indicating the start of the medium protection operation, BSS identification information for identifying a BSS to which a transmission-source wireless communication apparatus of the frame indicating the start of the medium protection operation belongs, and a transmission unit that determines whether or not to start a transmission operation of a frame addressed to another wireless communication apparatus belonging to a BSS to which the wireless communication apparatus belongs based on the BSS identification information.

TECHNICAL FIELD

The present invention relates to a wireless communication apparatus, acommunication method, and a communication system.

BACKGROUND ART

The Institute of Electrical and Electronics Engineers Inc. (IEEE)802.11ac which achieves a higher data rate in IEEE 802.11 which is awireless local area network (LAN) standard is developed by the IEEE.Currently, standardization of IEEE 802.11ax is started as the succeedingstandard of IEEE 802.11ac. As wireless LAN devices have been propagatedrapidly, even in the standardization of IEEE 802.11ax, the improvementof throughput for each user in an environment has been examined in whichthe wireless LAN devices are overcrowded.

The wireless LAN device monitors a preamble defined in IEEE 802.11, anddemodulates a physical layer convergence protocol (PLCP) header or adata signal in a case where the preamble is detected. For example, asthe preamble defined in IEEE 802.11, there are legacy-short trainingsequence (L-STF) and legacy-long training sequence (L-LTF). An operationneeded to demodulate a data signal such as synchronization or channelestimation may be performed by using these preambles.

The wireless LAN device detects the preamble, and then receives the PLCPheader. The PLCP header includes information (modulation and codingscheme (MCS) or the like) needed to demodulate the data signalsubsequent thereto. PLCP headers are differently defined depending onthe types of the IEEE 802.11 standards such as a high throughput-signal(HT-SIG) defined in IEEE 802.11n and a very high throughput-signal(VHT-SIG) defined in IEEE 802.11ac. Meanwhile, as a mechanism forprotecting a terminal apparatus (legacy terminal apparatus)corresponding to the conventional standard (IEEE 802.11a/b/g or thelike), legacy-signal (L-SIG) is generally inserted after L-LTF.

For example, the L-SIG may include information regarding a signaltransmission period of a transmission frame including the L-SIG. Thewireless LAN device that receives the L-SIG including the informationregarding the signal transmission period may acquire information forconfiguring a network allocation vector (NAV) without receiving the datasignal subsequent to the L-SIG.

As stated above, since the preamble and the PLCP header include variousinformation items such as information regarding the signal transmissionperiod or the demodulation of the data signal, the wireless LAN deviceneeds to detect the preamble and the PLCP header with high accuracy.

CITATION LIST Patent Literature

-   PTL 1: Japanese Unexamined Patent Application Publication    (Translation of PCT Application) No. 2015-515237

Non Patent Literature

-   NPL 1: IEEE 802.11-15/0588r0 May 2015

SUMMARY OF INVENTION Technical Problem

In PTL 1 and NPL 1, in the environment in which the wireless LAN devicesare overcrowded, a reduction in throughput caused by an exposed terminalproblem is pointed out. The exposed terminal problem is a problem thatthe access to the wireless medium is restricted due to interference fromthe adjacent device of a wireless LAN device as a transmission source.In this case, even though another wireless LAN device is not presentadjacent to the wireless LAN device as the transmission destination, thetransmission of the frame in the wireless LAN device may be suppressed,and user throughput may be reduced. However, in the wireless LAN systembased on CSMA/CA, it is very difficult to avoid the reduction in thethroughput caused by the exposed terminal problem.

The present invention has been made in view of the above-describedproblems, and it is an object of the invention to disclose a wirelesscommunication apparatus, a communication method, and a communicationsystem which realizes the improvement in user throughput by relaxing therestriction of the access of a wireless communication apparatus to awireless medium caused by an exposed terminal in order to improve theutilization efficiency of a radio resource of the communication system.

Solution to Problem

A wireless communication apparatus, a communication method, and acommunication system according to the present invention for solving theabove-described problems are as follows.

(1) That is, a wireless communication apparatus according to the presentinvention is a wireless communication apparatus capable of transmittingand receiving a physical layer frame. The apparatus includes a receptionunit that receives a frame indicating start of a medium protectionoperation, and acquires, from the frame indicating the start of themedium protection operation, BSS identification information foridentifying a BSS to which a transmission-source wireless communicationapparatus of the frame indicating the start of the medium protectionoperation belongs, and a transmission unit that determines whether ornot to start a transmission operation of a frame addressed to anarbitrary wireless communication apparatus based on the BSSidentification information.

(2) In the wireless communication apparatus according to the presentinvention described in (1), the transmission unit starts thetransmission operation of the frame addressed to the arbitrary wirelesscommunication apparatus in a case where the BSS identificationinformation indicates that the frame indicating the start of the mediumprotection operation is transmitted from a wireless communicationapparatus connected to a BSS other than the BSS to which the wirelesscommunication apparatus is connected.

(3) In the wireless communication apparatus according to the presentinvention described (2), the transmission unit prohibits the start ofthe transmission operation of the frame addressed to the arbitrarywireless communication apparatus for a period during which it isexpected that the transmission-source wireless communication apparatusof the frame indicating the start of the medium protection operation isto receive a frame within a period during which the medium protectionoperation is reserved.

(4) In the wireless communication apparatus according to the presentinvention described in (2), in a case where the frame addressed to thearbitrary wireless communication apparatus is a frame for requesting aframe reply and a period during which the frame reply is expectedmatches a period during which the transmission-source wirelesscommunication apparatus of the frame indicating the start of the mediumprotection operation performs frame transmission in whole or part withina period during the medium protection operation is reserved, the startof the transmission operation of the frame addressed to the arbitrarywireless communication apparatus is prohibited.

(5) In the wireless communication apparatus according to the presentinvention described in (1), the BSS identification information isinformation indicating a destination wireless communication apparatus ofthe frame indicating the start of the medium protection operation. Thereception unit retains a TA address set which is a set of informationitems indicating transmission-source wireless communication apparatusesof previously received frames, and the transmission unit starts thetransmission operation of the frame addressed to the arbitrary wirelesscommunication apparatus in a case where the information indicating thedestination wireless communication apparatus of the frame indicating thestart of the medium protection operation is not present in the TAaddress set.

(6) In the wireless communication apparatus according to the presentinvention described any one of (1) to (3), the frame indicating thestart of the medium protection operation is a CTS-to-self frame.

(7) In the wireless communication apparatus according to the presentinvention described in (4) or (5), the frame indicating the start of themedium protection operation is an RTS frame.

(8) A communication method according to the present invention is acommunication method of a wireless communication apparatus capable oftransmitting and receiving a physical layer frame. The method includes astep of receiving a frame indicating start of a medium protectionoperation, a step of acquiring, from the frame indicating the start ofthe medium protection operation, BSS identification information foridentifying a BSS to which a transmission-source wireless communicationapparatus of the frame indicating the start of the medium protectionoperation belongs, and a step of determining whether or not to start atransmission operation of a frame addressed to an arbitrary wirelesscommunication apparatus based on the BSS identification information.

(9) A communication system according to the present invention is acommunication system including a first wireless communication apparatusand a second wireless communication apparatus which are capable oftransmitting and receiving a physical layer frame. The first wirelesscommunication apparatus includes a transmission unit that transmits aframe, which indicates start of a medium protection operation andincludes BSS identification information for identifying a BSS to whichthe first wireless communication apparatus belongs. The second wirelesscommunication apparatus includes a reception unit that receives theframe indicating start of the medium protection operation, and acquiresthe BSS identification information for identifying the BSS to which thefirst wireless communication apparatus from the frame indicating thestart of the medium protection operation, and a transmission unit thatdetermines whether or not to start a transmission operation of a frameaddressed to an arbitrary wireless communication apparatus based on theBSS identification information.

Advantageous Effects of Invention

According to the present invention, it is possible to relax the accessrestriction of the wireless communication apparatus to the wirelessmedium which is caused by another adjacent wireless communicationapparatus, and thus, it is possible to contribute to the improvement ofthe throughput of the wireless communication apparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an example of a frame structure according tothe present invention.

FIG. 2 is a diagram showing an example of a frame structure according tothe present invention.

FIG. 3 is a diagram showing an example of communication according to thepresent invention.

FIG. 4 is a diagram showing a structure example of a communicationsystem according to the present invention.

FIG. 5 is a block diagram of a structure example of a wirelesscommunication apparatus according to the present invention.

FIG. 6 is a block diagram of a structure example of a wirelesscommunication apparatus according to the present invention.

FIG. 7 is a sequence chart showing an example of communication accordingto the present invention.

FIG. 8 is a diagram showing an example of communication according to thepresent invention.

FIG. 9 is a diagram showing an example of communication according to thepresent invention.

FIG. 10 is a sequence chart showing an example of communicationaccording to the present invention.

FIG. 11 is a diagram showing an example of a communication parameteraccording to the present invention.

FIG. 12 is a diagram showing an example of communication according tothe present invention.

DESCRIPTION OF EMBODIMENTS

A communication system according to the present embodiment includes awireless transmission apparatus (an access point or a base stationapparatus) and a plurality of wireless reception apparatuses (stationsand terminal apparatuses). A network including the base stationapparatus and the terminal apparatuses is referred to as a Basic ServiceSet (BSS: management range). The base station apparatus and the terminalapparatus are referred to as a wireless communication apparatus or awireless apparatus.

It is assumed that the base station apparatus and the terminalapparatuses within the BSS communicate with each other based on carriersense multiple access with collision avoidance (CSMA/CA). Although itwill be described in the present embodiment that an infrastructure modein which the base station apparatus communicates with a plurality ofterminal apparatuses is used, a method of the present embodiment may beperformed in an ad hoc mode in which the terminal apparatuses directlycommunicate with each other. In the ad hoc mode, the terminal apparatusconstitutes the BSS instead of the base station apparatus. The BSS inthe ad hoc mode is also referred to as an Independent Basic Service Set(IBSS). Hereinafter, the terminal apparatus constituting the IBSS in thead hoc mode may be regarded as the base station apparatus.

In an IEEE 802.11 system, the apparatuses may transmit multiple frametypes of transmission frames having a common frame format. Thetransmission frames are defined by a physical (PHY) layer, a mediumaccess control (MAC) layer, and a logical link control (LLC) layer.

The transmission frame of the PHY layer is referred to as a physicalprotocol data unit (PPDU: PHY protocol data unit or physical layerframe). The PPDU includes a physical layer header (PHY header) includingheader information for performing signal processing in the physicallayer and a physical service data unit (PSDU: PHY service data unit orMAC layer frame) which is a data unit processed in the physical layer.The PSDU may be constituted by an aggregated MPDU (A-MPDU) acquired byaggregating a plurality of MAC protocol data units (MPDUs) which isretransmission units in a wireless section.

The PHY header includes reference signals such as a short training field(STF) used for detecting and synchronizing signals and a long trainingfield (LTF) used for acquiring channel information for demodulating dataand control signals such as a signal (SIG) including control informationfor demodulating data. The STF is classified into Legacy-STF (L-STF),High throughput-STF (HT-STF), Very high throughput-STF (VHT-STF), andHigh efficiency-STF (HE-STF) according to the corresponding standards.Similarly, the LTF is classified into L-LTF, HT-LTF, VHT-LTF, andHE-LTF, and the SIG is classified into L-SIG, HT-SIG, VHT-SIG, andHE-SIG. The VHT-SIG is classified into VHT-SIG-AT and VHT-SIG-B.

The PHY header may include information (hereinafter, also referred to asBSS identification information) for identifying a BSS of a transmissionsource of the transmission frame. For example, the information foridentifying the BSS may be a service set identifier (SSID) of the BSS ora MAC address of the base station apparatus of the BSS. The informationfor identifying the BSS may be a value (for example, BSS color) specificto the BSS other than the SSID or the MAC address.

The PPDU is modulated according to the corresponding standard. Forexample, the PPDU is modulated into an orthogonal frequency divisionmultiplexing (OFDM) signal in a case where the IEEE 802.11n standard isused.

The MPDU includes a MAC layer header (MAC header) including headerinformation for performing signal processing in the MAC layer, a MACservice data unit (MSDU) which is a data unit processed in the MAC layeror a frame body, and a frame check sequence (FCS) for checking whetheror not an error occurs in the frame. A plurality of MSDUs may beaggregated as an aggregated MSDU (A-MSDU).

The frame type of the transmission frame of the MAC layer is largelyclassified into three data frames including a management frame formanaging a connection mode between the apparatuses, a control frame formanaging a communication mode between the apparatuses, and a data frameincluding actual transmission data, and these frame types are furtherclassified into multiple types of subframe types. The control frameincludes a reception completion notification (acknowledge (Ack)) frame,a transmission request (request to send (RTS)) frame, and a receptionpreparation completion (clear to send (CTS)) frame. The management frameincludes a beacon frame, a probe request frame, a probe response frame,an authentication frame, an association request frame, and anassociation response frame. The data frame includes a data frame and apolling (CF-poll) frame. Each apparatus may recognize a frame type and asubframe type of the received frame by reading the content of a framecontrol field included in the MAC header.

Ack may include Block Ack. Block Ack may be acknowledged to theplurality of MPDUs.

The beacon frame includes a field in which a beacon interval at whichbeacons are transmitted or the SSID is written. The base stationapparatus may periodically broadcast the beacon frame within the BSS,and the terminal apparatus may recognize the base station apparatus nearthe terminal apparatus by receiving the beacon frame. A case where theterminal apparatus recognizes the base station apparatus based on thebeacon frame broadcast from the base station apparatus is referred to aspassive scanning. Meanwhile, a case where the terminal apparatus probesthe base station apparatus by broadcasting the probe request framewithin the BSS is referred to as active scanning. The base stationapparatus may transmit the probe response frame as a response to theprobe request frame, and the written content of the probe response framemay be equivalent to the beacon frame.

The terminal apparatus recognizes the base station apparatus, and thenperforms a process of connection establishment with the base stationapparatus. The process of connection establishment is classified into anauthentication procedure and an association procedure. The terminalapparatus transmits the authentication frame (authentication request) tothe base station apparatus desired to be connected. In a case where theauthentication frame is received, the base station apparatus transmitsthe authentication frame (authentication response) including a statuscode indicating whether or not the terminal apparatus is authenticatedto the terminal apparatus. The terminal apparatus may determine whetheror not the authentication of the terminal apparatus is permitted by thebase station apparatus by reading the status code written in theauthentication frame. The base station apparatus and the terminalapparatus may exchange the authentication frame multiple number oftimes.

Subsequently to the authentication procedure, the terminal apparatustransmits the association request frame in order to perform theassociation procedure with the base station apparatus. In a case wherethe association request frame is received, the base station apparatusdetermines whether or not to permit the connection of the terminalapparatus, and transmits the association response frame in order tonotify the terminal apparatus of the determination result. In additionto a status code indicating whether or not the connection process isperformed, an association identifier (AID) for identifying the terminalapparatus is written in the association response frame. The base stationapparatus may manage the plurality of terminal apparatuses byconfiguring different AIDs to the terminal apparatuses for which theconnection is permitted.

After the connection process is performed, the base station apparatusand the terminal apparatus perform actual data transmission. In the IEEE802.11 system, a distributed coordination function (DCF), a pointcoordination function (PCF), an enhanced function (enhanced distributedchannel access (EDCA)) thereof, and a hybrid coordination function (HCF)are defined. Hereinafter, an example in which the base station apparatustransmits signals to the terminal apparatus in the DCF will bedescribed.

In the DCF, the base station apparatus and the terminal apparatusperform carrier sensing (CS) for checking a utilization situation ofradio channels near the base station apparatus and the terminalapparatus before communication is performed. For example, in a casewhere a signal of which a clear channel assessment level (CCA level) ishigher than a predetermined clear channel assessment level is receivedon the radio channel, the base station apparatus which is a transmissionstation postpones the transmission of the transmission frame on theradio channel. Hereinafter, in the radio channel, a state in which thesignal of which the CCA level is equal to or greater than thepredetermined CCA level is detected is referred to as a busy mode, and astate in which the signal of which the CCA level is equal to or greaterthan the predetermined CCA level is not detected is referred to as anidle mode. As stated above, the CS performed based on power (receivedpower level) of the signal actually received by each apparatus isreferred to as physical carrier sensing (physical CS). The CCA level isalso referred to as a carrier sensing level (CS level) or a CCAthreshold (CCAT). In a case where the signal of which the CCA level isequal to or greater than the predetermined CCA level is detected, thebase station apparatus and the terminal apparatus perform an operationfor demodulating at least the signal of the PHY layer.

The base station apparatus performs the carrier sensing by only an interframe space (IFS) corresponding to the type of the transmission frame tobe transmitted, and determines whether the radio channel is in the busymode or the idle mode. Periods during which the base station apparatusperforms the carrier sensing are different depending on the frame typesand the subframe types of the transmission frames to be transmitted bythe base station apparatus. In the IEEE 802.11 system, a plurality ofIFSs of which periods are different from each other is defined. Thereare a short inter frame space (SIFS: short IFS) used for thetransmission frame to which the highest priority is given, a pollinginter frame space (PCF IFS: PIFS) used for the transmission frame towhich the relatively high priority is given, and a distribution controlinter frame space (DCF IFS: DIFS) used for the transmission frame towhich the lowest priority is given. In a case where the base stationapparatus transmits the data frame in the DCF, the base stationapparatus uses the DIFS.

After the base station apparatus is on standby for the DIFS, and isfurther on standby for a random backoff time for avoiding framecollision. In the IEEE 802.11 system, a random backoff time called acontention window (CW) is used. In CSMA/CA, it is assumed that atransmission frame transmitted by a certain transmission station isreceived by a reception station in a state in which there is nointerference from another transmission station. Thus, in a case wherethe transmission stations transmit the transmission frames in the sametiming, the frames collide with each other, and thus, the receptionstations are not able to correctly receive the frames. Before thetransmission stations start the transmission, the transmission stationsare on standby for a randomly configured time, and thus, the framecollision is avoided. In a case where it is determined that the radiochannel is in the idle mode through the carrier sensing, the basestation apparatus may start to count down the CW, may initially acquirea transmission right when the CW becomes zero, and may transmit thetransmission frame to the terminal apparatus. In a case where it isdetermined that the radio channel is in the busy mode through thecarrier sensing for a period during which the CW is counted down, thebase station apparatus stops counting down the CW. In a case where theradio channel is in the idle mode, the base station apparatus restartscounting down the remaining CW subsequently to the previous IFS.

The terminal apparatus which is the reception station receives thetransmission frame, reads the PHY header of the transmission frame, anddemodulates the received transmission frame. The terminal apparatus mayrecognize whether or not the transmission frame is addressed to theterminal apparatus by reading the MAC header of the demodulated signal.The terminal apparatus may determine the destination of the transmissionframe based on information (for example, a group identifier (GID: groupID) written in the VHT-SIG-A) written in the PHY header.

The terminal apparatus determines that the received transmission frameis addressed to the terminal apparatus, and needs to transmit an ACKframe indicating that the frame is correctly received to the basestation apparatus which is the transmission station in a case where thetransmission frame is demodulated without error. The ACK frame is one ofthe transmission frames having the highest priority transmitted afterthe base station apparatus is on standby only for the SIFS period (therandom backoff time is not taken). The base station apparatus receivesthe ACK frame transmitted from the terminal apparatus, and ends a seriesof communication operations. In a case where the terminal apparatus doesnot correctly receive the frame, the terminal apparatus does nottransmit the ACK. Accordingly, in a case where the ACK frame is notreceived from the reception station for a predetermined period (SIFS+ACKframe length) after the frame is transmitted, the base station apparatusdetermines that the communication fails, and ends the communication. Asmentioned above, the end of the communication (also referred to as aburst) performed once in the IEEE 802.11 system needs to be determineddepending on whether or not the ACK frame is received except for aspecial case such as a case where a broadcast signal such as a beaconframe is transmitted or a case where fragmentation for dividing thetransmission data is used.

In a case where it is determined that the received transmission frame isnot addressed to the terminal apparatus, the terminal apparatusconfigures a network allocation vector (NAV) based on the length of thetransmission frame written in the PHY header. The terminal apparatusdoes not attempt communication for a period configured for the NAV. Thatis, since the terminal apparatus performs the same operation as in acase where it is determined that the radio channel is in the busy modethrough the physical CS for a period configured for the NAV,communication control using the NAV is also referred to as virtualcarrier sensing (virtual CS). In addition to the case where the NAV isconfigured based on the information written in the PHY header, the NAVis also configured based on the clear to send (CTS) frame or the requestto send (RTS) frame introduced in order to resolve a hidden terminalproblem.

Each apparatus performs the carrier sensing and autonomously acquiresthe transmission right in the DCF, whereas a control station called apoint coordinator (PC) controls the transmission right of each apparatuswithin the BSS in the PCF. In general, the base station apparatus is thePC, and acquires the transmission right of the terminal apparatus withinthe BSS.

A communication period of the PCF includes a contention free period(CFP) and a contention period (CP). Communication is performed based onthe above-described DCF for the CP, and the PC controls the transmissionright for the CFP. The base station apparatus which is the PC broadcaststhe beacon frame in which the period (CFP max duration) of the CFP iswritten within the BSS before the communication of the PCF is performed.The PIFS is used in the transmission of the beacon frame broadcast in acase where the transmission of the PCF is started, and is transmittedwithout waiting for the CW. The terminal apparatus that receives thebeacon frame configures the period of the CFP written in the beaconframe for the NAV. The terminal apparatus may acquire the transmissionright only in a case where a signal (for example, a data frame includingCF-poll) for signaling the acquisition of the transmission righttransmitted from the PC is received until the NAV elapses or a signal(for example, a data frame including CF-end) for broadcasting the end ofthe CFP within the BSS is received. Since the collision of the packetswithin the same BSS does not occur within the period of the CFP, eachterminal apparatus does not use the random backoff time used in the DCF.

Hereinafter, the base station apparatus and the terminal apparatus arereferred to as the wireless communication apparatus. Informationexchanged in a case where a certain wireless communication apparatuscommunicates with another wireless communication apparatus is alsoreferred to as data. That is, the wireless communication apparatusincludes the base station apparatus and the terminal apparatus.

The wireless communication apparatus has any one or both of a functionof transmitting the PPDU and a function of receiving the PPDU. FIG. 1 isa diagram showing an example of the structure of the PPDU transmitted bythe wireless communication apparatus. The PPDU corresponding to the IEEE802.11a/b/g standard includes L-STF, L-LTF, L-SIG, and a MAC frame (apayload, a data portion, data, or an information bit). The PPDUcorresponding to the IEEE 802.11n standard includes L-STF, L-LTF, L-SIG,HT-SIG, HT-STF, HT-LTF, and a MAC frame. The PPDU corresponding to theIEEE 802.11ac standard includes L-STF, L-LTF, L-SIG, VHT-SIG-A, VHT-STF,VHT-LTF, VHT-SIG-B, and a MAC frame in whole or part.

The L-STF, the L-LTF, and the L-SIG surrounded by the dotted line ofFIG. 1 are used commonly to the IEEE 802.11 standards (hereinafter, theL-STF, the L-LTF, and the L-SIG are also referred to as an L-header).That is, for example, the wireless communication apparatus correspondingto the IEEE 802.11a/b/g standard may appropriately receive the L-headerwithin the PPDU corresponding to the IEEE 802.11n/ac standard. Thewireless communication apparatus corresponding to the IEEE 802.11a/b/gstandard may receive the PPDU corresponding to the IEEE 802.11n/acstandard as the PPDU corresponding to the IEEE 802.11a/b/g standard.

However, since the wireless communication apparatus corresponding to theIEEE 802.11a/b/g standard is not able to demodulate the PPDUcorresponding to the IEEE 802.11n/ac standard, which is subsequent tothe L-header, this wireless communication apparatus is not able todemodulate information regarding a Duration/ID field used in theconfiguration of the NAV, a transmitter address (TA), or a receiveraddress (RA).

As a method for causing the wireless communication apparatuscorresponding to the IEEE 802.11a/b/g standard to appropriatelyconfigure the NAV (or to perform a reception operation for a prescribedperiod), the IEEE 802.11 prescribes a method of inserting Durationinformation into the L-SIG. Information (RATE field, L-RATE field,L-RATE, L_DATARATE, or L_DATARATE field) regarding a transmission speedwithin the L-SIG and information (LENGTH field, L-LENGTH field, orL-LENGTH) regarding a transmission period are used in order for thewireless communication apparatus corresponding to the IEEE 802.11a/b/gstandard to appropriately configure the NAV.

FIG. 2 is a diagram showing an example of the method of inserting theDuration information into the L-SIG. FIG. 2 shows an example of theconfiguration of the PPDU corresponding to the IEEE 802.11ac standard,and the configuration of the PPDU is not limited thereto. Theconfiguration of the PPDU corresponding to the IEEE 802.11n standard andthe configuration of the PPDU corresponding to the IEEE 802.11axstandard may be used. TXTIME includes information regarding a length ofthe PPDU, aPreambleLength includes information regarding the length of apreamble (L-STF+L-LTF), and aPLCPHeaderLength includes informationregarding a length of a PLCP header (L-SIG). The following Expression(1) is an expression showing an example of a method of calculatingL_LENGTH.

$\begin{matrix}{\mspace{20mu} \left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack} & \; \\{{{L\_ LENGTH} = {{\left\lceil \frac{\left( {{TXTIME} - {SE}} \right) - \left( {{aPLength} + {aPLCPHLength}} \right.}{aSymbolLength} \right\rceil \times N_{ops}} - \left\lceil \frac{\left( {{aPLCPSLength} + {{aPLCPConv}.{TailLength}}} \right.}{8} \right\rceil}}\mspace{20mu} {{SE} = {SignalExtension}}\mspace{20mu} {{aPLenght} = {aPreambleLength}}\mspace{20mu} {{aPLCPHLength} = {aPLCPHeaderLength}}\mspace{20mu} {{aPLCPSLength} = {aPLCPServiceLength}}\mspace{20mu} {{{aPLCPConv}.{TailLength}} = {aPLConvolutionalTailLength}}} & (1)\end{matrix}$

In this expression, SignalExtension is, for example, a virtual periodconfigured in order to achieve compatibility between the IEEE 802.11standards, and Nops is information associated with L_RATE. Therelationship between the Nops and the L_RATE is represented in FIG. 10.aSymbolLength is information regarding a period of one symbol (OFDMsymbol), aPLCPServiceLength is the number of bits included in a PLCPService field, and aPLCPConvolutionalTailLength is the number of tailbits of a convolutional code. For example, the wireless communicationapparatus may calculate L_LENGTH by using Expression (1), and may insertthe calculated L_LENGTH into the L-SIG. The method of calculating theL_LENGTH is not limited to Expression (1). For example, the L_LENGTH maybe calculated by using the following Expression (2).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack & \; \\{{L\_ LENGTH} = {{\left\lceil \frac{\left( {\left( {{TXTIME} - {SignalExtension}} \right) - 20} \right.}{4} \right\rceil \times 3} - 3}} & (2)\end{matrix}$

In a case where the PPDU is transmitted by L-SIG TXOP Protection, thewireless communication apparatus calculates the L_LENGTH by using thefollowing Expression (3) or the following Expression (4).

$\begin{matrix}{\mspace{20mu} \left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack} & \; \\{{L\_ LENGTH} = {{\left\lceil \frac{\left( {{L\text{-}{SIGDuration}} - {SE}} \right) - \left( {{aPLength} + {aPLCPHLength}} \right.}{aSymbolLength} \right\rceil \times N_{ops}} - \left\lceil \frac{\left( {{aPLCPSLength} + {{aPLCPConv}.{TailLength}}} \right.}{8} \right\rceil}} & (3) \\{\mspace{20mu} \left\lbrack {{Expression}\mspace{14mu} 4} \right\rbrack} & \; \\{{L\_ LENGTH} = {{\left\lceil \frac{\left( {\left( {{L\text{-}{SIGDuration}} - {SignalExtension}} \right) - 20} \right)}{4} \right\rceil \times 3} - 3}} & (4)\end{matrix}$

In these expressions, L-SIG Duration is, for example, informationregarding a period acquired by adding up the period of the PPDUincluding the L_LENGTH calculated by using Expression (3) or Expression(4) and the periods of the Ack and the SIFS to be expected to betransmitted, as a response, from the wireless communication apparatus asthe destination. The wireless communication apparatus calculates theL-SIG Duration by using the following Expression (5) or the followingExpression (6).

[Expression 5]

L-SIGDurtion=(T _(init) _(_)_(PPDU)−(aPreamMeLength+aPLPHeaderLength))+SIFS+T _(Res) _(_)_(PPDU)  (5)

[Expression 6]

L-SIGDuration=T _(MACDur)−SIFS−(aPreambleLength+aPLCPHeaderLength)  (6)

In these expressions, Tinit_PPDU is information regarding the period ofthe PPDU including L_LENGTH calculated by using the following Expression(5), and TRes_PPDU is information regarding the period of the PPDU to beexpected to be transmitted, as the response to the PPDU includingL_LENGTH calculated by using Expression (5). TMACDur is informationassociated with a value of a Duration/ID field included in the MAC framewithin the PPDU including L_LENGTH calculated by using Expression (6).The wireless communication apparatus calculates the L_LENGTH by usingExpression (5) in a case where the wireless communication apparatus isan initiator (sender, leader, or transmitter), and the wirelesscommunication apparatus calculates the L_LENGTH by using Expression (6)in a case where the wireless communication apparatus is a responder(receiver).

FIG. 3 is a diagram showing an example of L-SIG Duration in L-SIG TXOPProtection. DATA (frame, payload, or data) includes any one or both ofthe MAC frame and the PLCP header. BA is Block Ack or Ack. The PPDU mayinclude L-STF, L-LTF, and L-SIG, and may further include any one or aplurality of DATA, BA, RTS, and CTS. Although it has been described inthe example shown in FIG. 3 that L-SIG TXOP Protection using RTS/CTS isused, CTS-to-Self may be used. In this example, MAC Duration is a periodindicated by the value of Duration/ID field. The initiator may transmita CF_End frame in order to notify of the end of the period of L-SIG TXOPProtection.

Next, a method of identifying the BSS from the frame received by thewireless communication apparatus will be described. In order for thewireless communication apparatus to identify the BSS from the receivedframe, it is preferable that the wireless communication apparatus thattransmits the PPDU inserts information (BSS color, BSS identificationinformation, or a value specific to the BSS) for identifying the BSSinto the PPDU.

The BSS identification information may be the SSID of the BSS to whichthe wireless communication apparatus belongs, may be the MAC address ofthe AP of the BSS to which the wireless communication apparatus belongs,or may be the GID. The BSS identification information may be informationincluding a plurality of states (color) autonomously selected by theBSS. The plurality of states may be configured through signaling from acertain wireless communication apparatus or a higher layer.

For example, the wireless communication apparatus may construct the PPDUsuch that the BSS identification information is added to L-LTF, HT-LTF,VHT-LTF, or HE-LTF (hereinafter, also referred to as LTF). The wirelesscommunication apparatus may perform different cyclic shifts on LTF basedon the value of the BSS identification information, or may use differentcoding schemes on LTF based on the value of the BSS identificationinformation. In a case where the cyclic shift is performed on LTF, it ispreferable that the same cyclic shift is performed on any one or both ofL-SIG and DATA subsequent to LTF in consideration of backwardcompatibility with the wireless communication apparatus corresponding tothe conventional IEEE 802.11 standard. It is preferable that a cyclicshift amount is an amount that does not exceed a size of guard interval(GI) (CP or Cyclic Prefix).

For example, the wireless communication apparatus may add the BSSidentification information to the L-SIG. For example, the wirelesscommunication apparatus may add the BSS identification informationwithin L_RATE within the L-SIG. L_RATE is constituted by 4-bitinformation bits, and transmission rates are mapped to these informationbits. FIG. 10 is a diagram showing an example of the correspondencebetween transmission rates and Index in the mapping using the 4-bitinformation bits. L_LENGTH/L_RATE is calculated as L_LATE, and thus,TXTIME or L-SIG Duration may be acquired.

Meanwhile, the L_LENGTH may be calculated by using any of Expression (1)to Expression (4). Particularly, in a case where L_LENGTH is calculatedby using any of Expression (1) and Expression (3), the values of theL_RATE and the L_LENGTH may be configured in view of the relationshipbetween the L_RATE and the Nops represented in FIG. 10. That is, thewireless communication apparatus may select the L_RATE from any of eighttransmission rates of FIG. 10. The wireless communication apparatus mayconfigure the L_RATE based on the value of the BSS identificationinformation.

For example, the wireless communication apparatus may perform quadraturephase shift keying (QPSK) modulation on the L-SIG. Although the IEEE802.11 standard prescribes that binary phase shift keying (BPSK)modulation is performed on the L-SIG, the wireless communicationapparatus may realize the QPSK modulation by inserting the informationbits into an imaginary axis (Q axis) while mapping the L-SIG to a realaxis (I-Axis). The wireless communication apparatus may insert the BSSidentification information to the imaginary axis. In a case where thewireless communication apparatus performs the QPSK modulation on theL-SIG, it is preferable that a transmit power of the L-LTF is configuredas a power half the L-SIG or a transmit power of the L-SIG is configuredas a value double the L-LTF in consideration of the backwardcompatibility with the wireless communication apparatus corresponding tothe conventional IEEE 802.11 standard.

The wireless communication apparatus may associate the BSSidentification information with the modulation scheme. For example, themodulation schemes of the symbols (HT-SIG, VHT-SIG-A, HE-SIG-A,HE-SIG-B, HE-STF, and HE-LTF) subsequent to the L-SIG may be associatedwith the information bits. That is, the wireless communication apparatusmay modulate the symbols subsequent to the L-SIG by using any of theBPSK modulation and the quadrature binary phase shift keying (QBPSK)modulation. The wireless communication apparatus on the reception sidemay measure whether or not the power of the symbol is biased to (thepower is distributed on) the real axis or the imaginary axis, and mayacquire the corresponding information bit.

For example, a case where the QBPSK modulation is performed on a firstsymbol subsequent to the L-SIG and the BPSK modulation is performed on asecond symbol subsequent to the L-SIG may be an information bit (0, 1).In this example, a BPSK modulation symbol may correspond to 1, and aQBPSK modulation symbol may correspond to 0.

For example, the wireless communication apparatus may interpret that thePPDU corresponds to the IEEE 802.11n standard in a case where aninformation bit (0, 0) is acquired by detecting (auto detection of) themodulation schemes of two symbols subsequent to the L-SIG.

For example, the wireless communication apparatus may interpret that thePPDU corresponds to the IEEE 802.11ac standard in a case where aninformation bit (1, 0) is acquired by detecting (auto detection of) themodulation schemes of two symbols subsequent to the L-SIG.

For example, the wireless communication apparatus may interpret that thePPDU corresponds to the IEEE 802.11a standard or the IEEE 802.11gstandard in a case where an information bit (1, 1) is acquired bydetecting (auto detection of) the modulation schemes of two symbolssubsequent to the L-SIG.

For example, the wireless communication apparatus may add the BSSidentification information items within the HT-SIG, the VHT-SIG, theHE-SIG-A, and the HE-SIG-B.

The wireless communication apparatus may not use the information items(0, 0), (1, 0), and (1, 1) in order to achieve the backwardcompatibility. The wireless communication apparatus may construct theinformation bits by using three or more symbols subsequent to the L-SIG.That is, the wireless communication apparatus may construct theinformation bits by using the symbols subsequent to the L-SIG, and maymap the BSS identification information items.

The wireless communication apparatus may transmit the L-SIG multiplenumber of times (L-SIG repetition). For example, the wirelesscommunication apparatus on the reception side receives the L-SIGtransmitted multiple number of times by using maximum ratio combining(MRC), and thus, the demodulation accuracy of the L-SIG is improved. Ina case where the reception of the L-SIG is correctly completed throughthe MRC, the wireless communication apparatus may interpret that thePPDU including the L-SIG is the PPDU corresponding to the IEEE 802.11axstandard.

The wireless communication apparatus may perform different cyclic shiftson the plurality of L-SIGs acquired through the L-SIG repetition basedon the value of the BSS identification information. The wirelesscommunication apparatus on the reception side may acquire the BSSidentification information by estimating the cyclic shift amount.

The wireless communication apparatus may perform a reception operationof a part (for example, the preamble, the L-STF, the L-LTF, and the PLCPheader prescribed by the IEEE 802.11) of the PPDU other than this PPDUeven during the reception operation of the PPDU (also referred to as adiplex reception operation). The wireless communication apparatus mayupdate information regarding a destination address, a transmissionsource address, or a period of PPDU or DATA in whole or part in a casewhere a part of the PPDU other than this PPDU is detected during thereception operation of the PPDU.

Ack and BA may also be referred to the response (response frame). Aprobe response, an authentication response, or an association responsemay be referred to as the response.

1. First Embodiment

FIG. 4 is a diagram showing an example of a wireless communicationsystem according to the present embodiment. A wireless communicationsystem 3-1 includes a wireless communication apparatus 1-1 and awireless communication apparatus 2-1. The wireless communicationapparatus 1-1 is also referred to as a base station apparatus 1-1, andthe wireless communication apparatus 2-1 is also referred to as aterminal apparatus 2-1. The wireless communication apparatus 1-1 and thewireless communication apparatus 2-1 are wirelessly connected, andmutually perform the transmission and reception of the PPDU. Thewireless communication system according to the present embodimentincludes a wireless communication system 3-2 in addition to the wirelesscommunication system 3-1. The wireless communication system 3-2 includesa wireless communication apparatus 1-2 and a wireless communicationapparatus 2-2. The wireless communication apparatus 1-2 is also referredto as a base station apparatus 1-2, and the wireless communicationapparatus 2-2 is also referred to as a terminal apparatus 2-2. Althougha case where the wireless communication system 3-1 and the wirelesscommunication system 3-2 constitute different BSSs has been described,this case does not mean that extended service sets (ESSs) are notdifferent. The ESS is a service set constituting a local area network(LAN). That is, the wireless communication apparatuses belonging to thesame ESS may be regarded as belonging to the same network from thehigher layer. The wireless communication systems 3-1 and 3-2 may furtherinclude a plurality of wireless communication apparatuses.

In the following description, it is assumed in FIG. 4 that signalstransmitted by the wireless communication apparatus 2-1 reach thewireless transmission apparatus 1-1 and the wireless communicationapparatus 2-2 but does not reach the wireless communication apparatus1-2. That is, in a case where the wireless communication apparatus 2-1transmits the signals by using a certain channel, the wirelesscommunication apparatus 1-1 and the wireless communication apparatus 2-2determine that this channel is in the busy mode but the wirelesscommunication apparatus 1-2 determines that this channel is in the idlemode. It is assumed that signals transmitted by the wirelesscommunication apparatus 2-2 reach the wireless transmission apparatus1-2 and the wireless communication apparatus 2-1 but does not reach thewireless communication apparatus 1-1. That is, in a case where thewireless communication apparatus 2-2 transmits the signals by using acertain channel, the wireless communication apparatus 1-2 and thewireless communication apparatus 2-1 determine that this channel is inthe busy mode but the wireless communication apparatus 1-1 determinesthat this channel is in the idle mode.

FIG. 5 is a diagram showing an example of an apparatus configuration ofthe wireless communication apparatus 1-1, 2-1, 1-2, or 2-2 (hereinafter,also referred to as a wireless apparatus 10-1). The wirelesscommunication apparatus 10-1 includes a higher layer unit 10001-1, anautonomous distribution control unit 10002-1, a transmission unit10003-1, a reception unit 10004-1, and an antenna unit 10005-1.

The higher layer unit 10001-1 may be connected to another network, andmay notify the autonomous distribution control unit 10002-1 ofinformation regarding traffic. For example, the information regardingthe traffic may be information addressed to another wirelesscommunication apparatus, or may be control information included in themanagement frame or the control frame.

FIG. 6 is a diagram showing an example of a unit structure of theautonomous distribution control unit 10002-1. The autonomousdistribution control unit 10002-1 includes a CCA unit 10002 a-1, abackoff unit 10002 b-1, and a transmission determination unit 10002 c-1.

The CCA unit 10002 a-1 may perform the mode determination (including thedetermination of busy or idle) of the radio resource by using any one orboth of information regarding a received signal power received throughthe radio resource and information (including decoded information)regarding the received signal, which are notified from the receptionunit. The CCA unit 10002 a-1 may notify the backoff unit 10002 b-1 andthe transmission determination unit 10002 c-1 of mode determinationinformation of the radio resource.

The backoff unit 10002 b-1 may perform backoff by using the modedetermination information of the radio resource. The backoff unit 10002b-1 has a function of generating the CW and counting down the CW. Forexample, the backoff unit may count down the CW in a case where the modedetermination information of the radio resource indicates the idle mode,and may stop counting down the CW in a case where the mode determinationinformation of the radio resource indicates the busy mode. The backoffunit 10002 b-1 may notify the transmission determination unit 10002 c-1of the value of the CW.

The transmission determination unit 10002 c-1 performs transmissiondetermination by using any one or both of the mode determinationinformation of the radio resource and the value of the CW. For example,in a case where the mode determination information of the radio resourceindicates the idle mode and the value of the CW is zero, thetransmission determination unit may notify the transmission unit 10003-1of transmission determination information. In a case where the modedetermination information of the radio resource indicates the idle mode,the transmission determination unit may notify the transmission unit10003-1 of the transmission determination information.

The transmission unit 10003-1 includes a physical layer frame generationunit 10003 a-1 and a wireless transmission unit 10003 b-1. The physicallayer frame generation unit 10003 a-1 has a function of generating thephysical layer frame (PPDU) based on the transmission determinationinformation notified from the transmission determination unit 10002 c-1.The physical layer frame generation unit 10003 a-1 performs errorcorrection coding, modulation, and precoding filter multiplication onthe transmission frame delivered from the higher layer. The physicallayer frame generation unit 10003 a-1 notifies the wireless transmissionunit 10003 b-1 of the generated physical layer frame.

The wireless transmission unit 10003 b-1 converts the physical layerframe generated by the physical layer frame generation unit 10003 a-1into a signal having a radio frequency (RF) band, and generates aradio-frequency signal. A process performed by the wireless transmissionunit 10003 b-1 includes digital-to-analog conversion, filtering, andfrequency conversion from a baseband to an RF band.

The reception unit 10004-1 includes a wireless reception unit 10004 a-1and a signal demodulation unit 10004 b-1. The reception unit 10004-1generates information regarding a received signal power from the signalhaving the RF band received by the antenna unit 10005-1. The receptionunit 10004-1 may notify the CCA unit 10002 a-1 of the informationregarding the received signal power and the information regarding thereceived signal.

The wireless reception unit 10004 a-1 has a function of converting thesignal having the RF band received by the antenna unit 10005-1 into abaseband signal and generating the physical layer signal (for example,physical layer frame). A process performed by the wireless receptionunit 10004 a-l includes a frequency conversion process from the RF bandto the baseband, filtering, and analog-to-digital conversion.

The signal demodulation unit 10004 b-1 has a function of demodulatingthe physical layer signal generated by the wireless reception unit 10004a-1. A process performed by the signal demodulation unit 10004 b-1includes channel equalization, demapping, and error correction decoding.For example, the signal demodulation unit 10004 b-1 may extractinformation included in the physical layer header, information includedin the MAC header, and information included in the transmission framefrom the physical layer signal. The signal demodulation unit 10004 b-1may notify the higher layer unit 10001-1 of the extracted information.The signal demodulation unit 10004 b-1 may extract any one or all of theinformation included in the physical layer header, the informationincluded in the MAC header, and the information included in thetransmission frame.

The antenna unit 10005-1 has a function of transmitting theradio-frequency signal generated by the wireless transmission unit 10003b-1 toward the wireless apparatus 0-1 in a wireless space. The antennaunit 10005-1 has a function of receiving the radio-frequency signaltransmitted from the wireless apparatus 0-1.

The wireless communication apparatus 10-1 may insert the BSSidentification information into the PPDU, and may transmit the PPDU inthe wireless space. Hereinafter, it will be described that the BSSidentification information items included in the PPDUs transmitted bythe wireless communication apparatus 1-1 and the wireless communicationapparatus 2-1 and the BSS identification information items transmittedby the wireless communication apparatus 1-2 and the wirelesscommunication apparatus 2-2 are different from each other. In a casewhere the wireless communication apparatuses 10-1 constitute the sameESS, the BSS identification information may be configured throughsignaling from any of the wireless communication apparatuses 10-1, thewireless communication apparatus other than the wireless communicationapparatus 10-1, or a higher layer apparatus. In a case where thewireless communication system 3-1 and the wireless communication system3-2 constitute different ESSs, the wireless communication apparatuses10-1 may autonomously configure the BSS identification informationitems. However, the method of configuring the BSS identificationinformation is not limited.

Since the wireless communication apparatus 1-1 and the wirelesscommunication apparatus 2-1 belong to the same BSS, it is preferablethat the same BSS identification information is used. Similarly, sincethe wireless communication apparatus 1-2 and the wireless communicationapparatus 2-2 belong to the same BSS, the beacon transmitted by thewireless communication apparatus 1-1 may be transmitted while includingthe BSS identification information or the information associated withthe BSS identification information, and the BSS identificationinformation may be acquired from the beacon received by the wirelesscommunication apparatus 2-1.

FIG. 7 is a sequence chart showing an example of communication accordingto the present embodiment. Hereinafter, an operation of the wirelesscommunication apparatus according to the present embodiment will bedescribed with reference to FIGS. 4 and 7.

Initially, the wireless communication apparatus 2-1 (a first wirelesscommunication apparatus or a transmission-source wireless communicationapparatus) performs a medium protection operation (protection procedure)or a medium reservation operation (reservation procedure) for reservinga wireless medium (WM) before the PPDU addressed to the wirelesscommunication apparatus 1-1 (destination wireless communicationapparatus) is transmitted (step S701). In this example, the mediumprotection operation or the medium reservation operation is notparticularly limited, and the wireless communication apparatus 2-1 maytransmit a CTS frame (CTS-to-self or Self-CTS) in which the MAC addressof the wireless communication apparatus 2-1 is written in the RA field.The wireless communication apparatus 2-1 may write the BSSidentification information in the CTS frame by the previously describedmethod.

Subsequently, the wireless communication apparatus 2-1 assumes that theCTS-to-self frame transmitted by the wireless communication apparatus isreceived (step S702 a) by the wireless communication apparatus withinthe BSS (including the wireless communication apparatus 1-1), transmitsthe CTS-to-self frame, and transmits the PPDU addressed to the wirelesscommunication apparatus 1-1 (step S703). Since the operation startedfrom step S703 is the same operation as the typical frame exchange, thedescription thereof will be omitted.

Meanwhile, the reception unit 10004-1 of the wireless communicationapparatus 2-2 (second wireless communication apparatus) may receive theCTS-to-self frame transmitted by the wireless communication apparatus2-1 which is the transmission-source wireless communication apparatus(step S702 b). In the conventional wireless LAN system in which the BSSidentification information is acquired based on the CTS-to-self (stepS704), in a case where the wireless communication apparatus 2-2 receivesthe CTS-to-self frame, the wireless communication apparatus 2-2configures the NAV, stops the reception operation, or prohibits thestart of the transmission operation based on the Duration informationwritten in the CTS-to-self frame. Meanwhile, the reception unit 10004-1and the transmission unit 10003-1 of the wireless communicationapparatus 2-2 according to the present embodiment determine the actualoperation based on the BSS identification information written in theCTS-to-self (step S705). For example, the reception unit 10004-1 maydetermine whether or not to stop the reception operation based on theBSS identification information. For example, the transmission unit10003-1 may determine whether or not to prohibit the start of thetransmission operation based on the BSS identification information. Theoperation of step S705 may be performed by the higher layer unit10001-1.

The medium protection operation and the medium reservation operationinclude RTS/CTS frame exchange, Dual CTS, L-SIG TXOP protection, andRIFS protection in addition to the transmission of the CTS-to-self framedescribed above. In a case where the medium protection operation is theRTS/CTS frame exchange, the frame indicating the start of the mediumprotection operation includes the RTS frame. The medium protectionoperation is the Dual CTS, the frame indicating the start of the mediumprotection operation includes the CTS frame or the CTS-to-self frame. Ina case where the medium protection operation is the L-SIG TXOPprotection, the frame indicating the start of the medium protectionoperation includes the frame including the PLCP header in which theDuration information is written by the previously described method.

The medium protection operation and the medium reservation operationinclude an initiation operation of the contention-free period used inthe PCF or hybrid coordination function (HCF). In this case, the frameindicating the start of the medium protection operation includes theframe (for example, beacon frame) including the information regardingthe period of the CFP. The medium protection operation includes apolling operation of the TXOP of the EDCA. In this case, the frameindicating the start of the medium protection operation includes a QoSCF-Poll frame or a frame (for example, QoS data+CF-Poll frame) havingthe CF-Poll function. The medium protection operation and the mediumreservation operation include a reservation operation of MCF controlledchannel access opportunity (MCCAOP) used in a mesh coordination function(MCF). In this case, the frame indicating the start of the mediumprotection operation includes a frame including a MCCAOP Setup Requestelement.

In a case where the frame indicating the start of the medium protectionoperation and the medium reservation operation is received, since thewireless communication apparatus 2-2 is able to acquire the BSSidentification information from the frame, the wireless communicationapparatus 2-2 determines whether a wireless communication apparatus thatstarts the medium protection operation and the medium reservationoperation is connected to the BSS to which the wireless communicationapparatus 2-2 is connected or is connected to an OBSS.

In a case where the wireless communication apparatus 2-2 according tothe present embodiment determines that the CTS-to-self frame is theframe transmitted from a wireless communication apparatus connected to aBSS (OBSS: overlapping BSS) other than the BSS to which the wirelesscommunication apparatus 2-2 is connected, the wireless communicationapparatus 2-2 may continue the reception operation irrespective of thevalue of the Duration information written in the CTS-to-self. Since thewireless transmission apparatus 2-1 recognizes the wirelesscommunication apparatus 1-2 to which the wireless communicationapparatus 2-2 is being connected as being in the mode of the hiddenterminal, there is a possibility that the wireless communicationapparatus 1-2 will start the transmission of the PPDU to the wirelesscommunication apparatus 2-2 irrespective of whether or not the wirelesscommunication apparatus 2-1 performs the medium protection operation.The wireless communication apparatus 2-2 continues the receptionoperation even after the CTS-to-self frame transmitted by the wirelesscommunication apparatus 2-1 is received, and thus, the wirelesscommunication apparatus 1-2 may receive the PPDU transmitted to thewireless communication apparatus 2-2.

The wireless communication apparatus 2-2 receives the PPDU transmittedfrom the wireless communication apparatus 1-2, and the wirelesscommunication apparatus 2-2 needs to transmit the ACK frame or the BAframe to the wireless communication apparatus 1-2 in a case where aframe for requesting a frame reply (for example, the reply of the ACKframe) is included in the PPDU. However, in a case where the wirelesscommunication apparatus 2-2 transmits the ACK frame for the period ofthe NAV calculated based on the value of the Duration informationwritten in the CTS-to-self frame, the ACK frame is also received by thewireless communication apparatus 2-1. Here, in a case where the wirelesscommunication apparatus 2-1 receives the PPDU (for example, the ACKframe transmitted from the wireless communication apparatus 1-1)transmitted from the wireless communication apparatus 1-1 in the WMreserved by the CTS-to-self frame, there is a possibility that thewireless communication apparatus 2-1 will fail to receive the PPDUtransmitted from the wireless communication apparatus 1-1 due tointerference caused by the ACK frame transmitted by the wirelesscommunication apparatus 2-2. Thus, in a case where the wirelesscommunication apparatus 2-2 needs to transmit a reply to the PPDUtransmitted from the wireless communication apparatus 1-2, the wirelesscommunication apparatus 2-2 may transmit the reply to the PPDU to thewireless communication apparatus 1-2 after the period of the NAVcalculated from the CTS-to-self is ended.

In a case where the wireless communication apparatus 2-2 according tothe present embodiment determines that the CTS-to-self frame is theframe transmitted from the wireless communication apparatus connected tothe OBSS, the wireless communication apparatus 2-2 may start thetransmission operation of the frame addressed to an arbitrary wirelesscommunication apparatus irrespective of the value of the Durationinformation written in the CTS-to-self. As described above, since thewireless transmission apparatus 2-1 recognizes the wirelesscommunication apparatus 1-2 to which the wireless communicationapparatus 2-2 is being connected as being in the mode of the hiddenterminal, even though the wireless communication apparatus 2-2 transmitsthe PPDU to the wireless communication apparatus 1-2 in a state in whichthe wireless communication apparatus 2-1 transmits the frame, thewireless communication apparatus 1-2 may receive the PPDU transmittedfrom the wireless communication apparatus 2-2 without interferencecaused by the frame transmitted by the wireless communication apparatus2-1.

The PPDU transmitted to the wireless communication apparatus 1-2 by thewireless communication apparatus 2-2 is also received by the wirelesscommunication apparatus 2-1. In this example, similarly to thepreviously described case, in a case where the wireless communicationapparatus 2-1 receives the PPDU (for example, the ACK frame transmittedfrom the wireless communication apparatus 1-1) transmitted from thewireless communication apparatus 1-1 in the WM reserved by theCTS-to-self frame, there is a possibility that the wirelesscommunication apparatus 2-1 will fail to receive the PPDU transmittedfrom the wireless communication apparatus 1-1 due to the interferencecaused by the PPDU transmitted by the wireless communication apparatus2-2. Thus, the wireless communication apparatus 2-2 may control suchthat the PPDU is transmitted only in a case where Duration (or length)of the PPDU transmitted by the wireless communication apparatus 2-2 isshorter than a period acquired by subtracting an ACK frame length and anSIFS length from Duration read from the CTS-to-self frame. The wirelesscommunication apparatus 2-2 prohibits the start of the transmissionoperation in a case where Duration (or length) of the PPDU transmittedby the wireless communication apparatus 2-2 is longer than a periodacquired by subtracting the ACK frame length and the SIFS length fromDuration read from the CTS-to-self frame.

In other words, the wireless communication apparatus 2-2 (or thereception unit 10004-1, the transmission unit 10003-1, and the higherlayer unit 10001-1 included in the wireless communication apparatus 2-2)determines whether or not the wireless communication apparatus 2-1 thatstarts the medium protection operation is an apparatus recognized as anexposed terminal apparatus by the wireless communication apparatus 2-2based on the information (in the above-described example, BSSidentification information) written in the frame (in the above-describedexample, CTS-to-self frame) indicating the start of the mediumprotection operation or the medium reservation operation. The wirelesscommunication apparatus 2-2 may determine whether or not the destinationwireless communication apparatus (in the above-described example, thewireless communication apparatus 1-1) indicated by the RA of the frametransmitted subsequently to the medium protection operation by thewireless communication apparatus 2-1 that starts the medium protectionoperation is the apparatus recognized as the hidden terminal apparatusby the wireless communication apparatus based on the information writtenin the frame indicating the start of the medium protection operation orthe medium reservation operation.

The wireless communication apparatus 2-2 according to the presentembodiment may determine whether or not to perform the receptionoperation of the wireless communication apparatus 2-2 or whether or notto start the transmission operation subsequently to the mediumprotection operation or the medium reservation operation of the wirelesscommunication apparatus 1-2 based on the information other than the BSSidentification information read from the medium protection operation orthe medium reservation operation of the wireless communication apparatus1-2. For example, the wireless communication apparatus 2-2 may retain aTA address written in the MAC header of the frame of the IEEE 802.11standard received by the wireless communication apparatus 2-2 in thepast. Hereinafter, a set of TA addresses retained in the wirelesscommunication apparatus 2-2 is referred to as a TA address set. Thewireless communication apparatus 2-2 may retain all the TA addressesfrom a point of time when the association process with the BSS to whichthe wireless communication apparatus 2-2 is being currently connected isstarted, or may retain the TA addresses for TBTT of the BSS to which thewireless communication apparatus 2-2 is being connected. The wirelesscommunication apparatus 1-2 may transmit the RTS frame in order toperform the medium reservation operation, and the wireless communicationapparatus 2-2 may read the RA address of the RTS frame in a case wherethe wireless communication apparatus 2-2 receives the RTS frame. Thewireless communication apparatus 2-2 may perform the reception operationand may start the transmission operation irrespective of the value ofthe NAV calculated from the RTS frame in a case where the RA address isnot present in the TA address set of the wireless communicationapparatus 2-2. This is because it is considered that the frametransmitted by the wireless communication apparatus 2-2 does not reachthe wireless communication apparatus specified by the RA address in acase where the RA address of the RTS frame is not present in the TAaddress set of the wireless communication apparatus 2-2. However, sincethe frame transmitted by the wireless communication apparatus 2-2reaches the wireless communication apparatus (in the above-describedexample, the wireless communication apparatus 2-1) that is performingthe medium protection operation or the medium reservation operation, itis preferable that the wireless communication apparatus 2-2 operates soas not to influence the reception operation of the wirelesscommunication apparatus. For example, in a case where the mediumprotection operation recognized by the wireless communication apparatus2-2 is the RTS/CTS frame exchange, the wireless communication apparatus2-2 may prohibit the start of the transmission operation for a periodduring which it is expected that the wireless communication apparatusthat transmits the RTS frame is to receive the CTS frame. In this case,the wireless communication apparatus 2-2 may interpret the RA address ofthe RTS frame as the BSS identification information. This is because itis interpreted that the wireless communication apparatus that is notpresent in the TA address set retained by the wireless communicationapparatus 2-2 is being connected to the OBSS.

FIG. 8 is a diagram showing an example of an operation of the wirelesscommunication apparatus 2-1. The PPDU includes the PLCP header and theMAC frame. The PLCP header includes a plurality of L-STF, L-LTF, L-SIG,HT-SIG, HT-STF, HT-STF, VHT-SIG-A, VHT-STF, VHT-LTF, VHT-SIG-B, HE-SIG,HE-SIG-A, HE-SIG-B, HE-LTF, and HE-LTF. In the example shown in FIG. 7,the wireless communication apparatus 1-2 initially transmits the PPDU.The wireless communication apparatuses 10-1 other than the wirelesscommunication apparatus 1-2 detect the preamble, and demodulate theL-SIG. In this example, it is assumed that the PPDU transmitted by thewireless communication apparatus 1-2 is detected by the wirelesscommunication apparatus 2-1 and the wireless communication apparatus2-2. The wireless communication apparatus 2-1 and the wirelesscommunication apparatus 2-2 may receive the PLCP header, and may acquirethe BSS identification information. The wireless communication apparatus2-2 may acquire the BSS identification information, and may recognizethat the PPDU belongs to the same BSS as that of the wirelesscommunication apparatus 2-2. The wireless communication apparatus 2-2may recognize that the MAC frame is addressed to the wirelesscommunication apparatus 2-2 by receiving the MAC frame within the DATA,and transmits the PPDU including the BA to the wireless communicationapparatus 1-2 after the wireless communication apparatus 2-2 is onstandby for the period of the SIFS after the reception of the MAC frameis completed.

Meanwhile, the wireless communication apparatus 2-1, that is, thewireless apparatus receives the PLCP header transmitted by the wirelesscommunication apparatus 1-2, and acquires the BSS identificationinformation. However, in the example shown in FIG. 8, the wirelesscommunication apparatus 2-1 continue to receive the PPDU transmitted bythe wireless communication apparatus 1-2 (or the wireless communicationapparatus 2-1 receives the PLCP header and ends the reception operationbut configures the NAV). Thus, since the wireless communicationapparatus 1-1 transmits the PPDU (for example, the PPDU addressed to thewireless communication apparatus 2-1) to be transmitted later than thePPDU transmitted by the wireless communication apparatus 1-2, thewireless communication apparatus 2-1 is not able to receive the PLCPheader within the PPDU. Accordingly, the detection rate of the PLCPheader of the wireless communication apparatus 2-1 is decreased, and theMAC frame within the DATA subsequent to the PLCP header is not able tobe demodulated.

FIG. 9 is a diagram showing another example of the operation of thewireless communication apparatus 2-1. Similarly to the example shown inFIG. 8, the wireless communication apparatus 2-1 initially demodulatesthe PLCP header transmitted by the wireless communication apparatus 1-2,and acquires the BSS identification information. Since the wirelesscommunication apparatus 2-1 recognizes that the PPDU is not addressed tothe BSS to which the wireless communication apparatus 2-1 belongs byacquiring the BSS identification information, the wireless communicationapparatus 2-1 ends the reception operation after the reception of thePLCP header is completed. Accordingly, the wireless communicationapparatus 2-1 may subsequently receive the PLCP header addressed to thewireless communication apparatus 2-1 transmitted from the wirelesscommunication apparatus 1-1 or the MAC frame within the DATA, and maydemodulate the received PLCP header or MAC address. Thereafter, thewireless communication apparatus 2-1 may be on standby for the period ofthe SIFS, and may transmit the PPDU including the BA to the wirelesscommunication apparatus 1-1.

As described above, the wireless communication apparatus may increaseutilization efficiency of the wireless communication system by changingthe reception operation based on the BSS identification information.

FIG. 10 is a sequence chart showing an example of the operation of thewireless communication apparatus 10-1. The wireless communicationapparatus 1-2 transmits the PLCP header transmitted by the wirelesscommunication apparatus 1-2 (step S101). The wireless communicationapparatus 2-1 receives the PLCP header transmitted by the wirelesscommunication apparatus 1-2, and performs reception operationdetermination (step S102). The method of the reception operationdetermination will be described below. Subsequently to step S101, thewireless communication apparatus 1-2 transmits the DATA (step S103).Thereafter, the wireless communication apparatus 1-1 transmits the PLCPheader (step S104). The wireless communication apparatus 2-1 receivesthe PLCP header transmitted by the wireless communication apparatus 1-1,and performs the reception operation determination (step S105).Subsequently to step S104, the wireless communication apparatus 1-1transmits the DATA (step S106). The wireless communication apparatus 2-1receives the DATA transmitted by the wireless communication apparatus1-1 (step S107).

The wireless communication apparatus 2-1 performs the receptionoperation determination. The reception operation determination is amethod of determining the method of the reception operation to besubsequently performed during the reception of the PPDU. For example,the wireless communication apparatus 2-1 performs the receptionoperation determination by using the BSS identification informationincluded in the PLCP header. In a case where the wireless communicationapparatus 2-1 determines that the PPDU is associated with the BSS towhich the wireless communication apparatus 2-1 belongs by using the BSSidentification information (also referred to as, for example, a casewhere it is determined that the PPDU is the signal addressed to thewireless communication apparatus belonging to the BSS, a case where thePPDU includes the same information as the BSS identification informationof the BSS, or a case where it is determined that the PPDU is associatedwith myBSS to be described below), the wireless communication apparatus2-1 performs the operation for continuing the reception operation.Alternatively, in a case where it is determined that the PPDU isassociated with the myBSS, the wireless communication apparatus 2-1configures the NAV. In a case where the wireless communication apparatus2-1 determines that the PPDU is not associated with the BSS to which thewireless communication apparatus 2-1 belongs by using the BSSidentification information (also referred to as, for example, a casewhere it is determined that the PPDU is the signal addressed to awireless communication apparatus other than the wireless communicationapparatus belonging to the BSS, a case where the PPDU includesinformation different from the BSS identification information of theBSS, or a case where it is determined that the PPDU is associated withthe overwrapped BSS (OBSS)), the wireless communication apparatus 2-1ends the reception operation.

In a case where the DATA subsequent to the L-SIG corresponds to the IEEE802.11ax standard, the wireless communication apparatus 2-1 may performthe reception operation determination. In a case where the DATAsubsequent to the L-SIG corresponds to the standard other than the IEEE802.11ax standard, the wireless communication apparatus 2-1 may notperform the reception operation determination.

In a case where it is determined that the PPDU is associated with theOBSS through the reception operation determination, the wirelesscommunication apparatus 2-1 may operate so as not to transmit the signalfor the TXTIME included in the L-SIG or the L-SIG Duration. The wirelesscommunication apparatus 2-1 does not transmit the signal for the TXTIMEor the L-SIG Duration period, but may detect the preamble or detect thePLCP header. Hereinafter, a case where the wireless communicationapparatus 2-1 does not transmit the signal but may detect the preambleor detect the PLCP header is also referred to as a receiver state. Forexample, the wireless communication apparatus 2-1 may configure thereceiver state.

In a case where it is determined that the PPDU is associated with theOBSS through the reception operation determination, the wirelesscommunication apparatus 2-1 may configure the receiver state. A periodof the receiver state may be configured by the TXTIME included in theL-SIG or the L-SIG Duration or may be configured by using the LENGTHfield included in the PLCP header within the DATA or informationassociated with a PPDU transmission period other than the LENGTH field.

In a case where it is determined that the PPDU is associated with theOBSS through the reception operation determination, the wirelesscommunication apparatus 2-1 may configure the NAV. In this case, thewireless communication apparatus 2-1 that configures the NAV may performthe reception operation unlike the typical NAV.

In a case where it is determined that the PPDU is associated with theOBSS through the reception operation determination, the wirelesscommunication apparatus 2-1 may be on standby for the transmission forthe IFS. The period of the IFS of the wireless communication apparatus2-1 may be configured by the TXTIME included in the L-SIG or the L-SIGDuration or may be configured by using the LENGTH field included in thePLCP header within the DATA or the information associated with the PPDUtransmission period other than the LENGTH field. Alternatively, thealready prescribed IFS period may be configured. For example, thewireless communication apparatus 2-1 may configure the IFS period byusing the TXTIME included in the L-SIG or the L-SIG Duration byrepeating the IFS. The wireless communication apparatus 2-1 may be onstandby for the transmission by the LENGTH field included in the PLCPheader within the DATA or the PPDU transmission period other than theLENGTH field or may be on standby for the transmission for AIFS.

In a case where it is determined that the PPDU is associated with theOBSS through the reception operation determination, the wirelesscommunication apparatus 2-1 may configure the backoff. The backoffperiod of the wireless communication apparatus 2-1 may be configured bythe TXTIME included in the L-SIG or the L-SIG Duration, or may beconfigured by the period corresponding to the LENGTH field included inthe PLCP header within the DATA or the PPDU transmission period otherthan the LENGTH field. The wireless communication apparatus 2-1 mayrepeat random backoff.

The wireless communication apparatus 2-1 may determine to configure theNAV or not to configure the NAV based on the reception operationdetermination. For example, in a case where it is determined that thePPDU is associated with the OBSS through the reception operationdetermination, the wireless communication apparatus 2-1 may notconfigure the NAV or may configure the NAV.

In a case where it is determined that the PPDU is associated with themyBSS through the reception operation determination, the wirelesscommunication apparatus 2-1 may not configure the NAV or may configurethe NAV.

The wireless communication apparatus 2-1 may perform the diplexreception operation in a case where it is determined that the PPDU isassociated with the myBSS through the reception operation determination,and may not perform the diplex reception operation in a case where it isdetermined that the PPDU is associated with the OBSS.

The wireless communication apparatus 2-1 may not perform the diplexreception operation in a case where it is determined that the PPDU isassociated with the myBSS through the reception operation determination,and may perform the diplex reception operation in a case where it isdetermined that the PPDU is associated with the OBSS.

FIG. 12 is a diagram showing an example of the operation of the wirelesscommunication apparatus 10-1. Initially, the wireless communicationapparatus 1-2 transmits the PLCP header. The wireless communicationapparatus 2-1 and the wireless communication apparatus 2-2 receive thePLCP header transmitted from the wireless communication apparatus 1-2,and acquire the BSS identification information. In the example shown inFIG. 12, it is assumed that the PPDU transmitted by the wirelesscommunication apparatus 1-2 is not detected in whole or part. Thewireless communication apparatus 2-2 determines that the PPDU isassociated with the myBSS by using the BSS identification information,and starts the reception of the DATA subsequent to the PLCP header. Inthis example, it is assumed that the PPDU transmitted by the wirelesscommunication apparatus 1-2 is addressed to the wireless communicationapparatus 2-2, and the wireless communication apparatus 2-2 may transmitthe BA to the wireless communication apparatus 1-2 in a case where thereception of a desired signal is correctly completed. In FIG. 11, atransmission end time of the BA transmitted by the wirelesscommunication apparatus 2-2 is referred to as a session end time (Ackend time, channel reservation period, or CCA busy period).

Meanwhile, the wireless communication apparatus 2-1 acquires the BSSidentification information, and determines that the PPDU is associatedwith the OBSS. Thus, the wireless communication apparatus 2-1 may endthe reception of the PPDU transmitted by the wireless communicationapparatus 1-2 through the reception operation determination.

It is assumed that the wireless communication apparatus 1-1 transmitsthe PPDU addressed to the wireless communication apparatus 2-1 after atime when the wireless communication apparatus 2-1 ends the reception ofa PPDU (also referred to as a first PPDU or a first physical layerframe) transmitted from the wireless communication apparatus 1-2. Thewireless communication apparatus 2-1 receives the PLCP header includedin a PPDU (also referred to as a second PPDU or a second physical layerframe) transmitted from the wireless communication apparatus 1-1. Thewireless communication apparatus 2-1 acquires the BSS identificationinformation, and performs the reception operation determination. As theresult of the reception operation determination, the wirelesscommunication apparatus 2-1 determines that the PPDU is associated withthe myBSS, and starts the reception operation of the DATA subsequent tothe PPDU.

Subsequently, the wireless communication apparatus 2-1 may performtransmission operation determination. The wireless communicationapparatus 2-1 may perform the transmission operation determination basedon information regarding the session end time and an Ack transmissionstart time. For example, the wireless communication apparatus 2-1 maydetermine to transmit the PPDU in a case where a session start timearrives earlier than the Ack transmission start time or arrives at thesame time as the Ack transmission start time, and the wirelesscommunication apparatus 2-1 may determine not to transmit the PPDU in acase where the session start time arrives later than the Acktransmission start time.

In a case where it is determined to transmit the PPDU through thetransmission operation determination, the wireless communicationapparatus 2-1 may transmit a PPDU (also referred to as a third PPDU or athird physical layer frame). The third PPDU may be the PPDU includingthe BA.

For example, through the transmission operation determination, thewireless communication apparatus 2-1 may determine not to transmit thePPDU in a case where the session start time arrives earlier than the Acktransmission start time or arrives at the same time as the Acktransmission start time, and the wireless communication apparatus 2-1may determine to transmit the PPDU in a case where the session starttime arrives later than the Ack transmission start time.

For example, the wireless communication apparatus 2-1 may determine totransmit the PPDU or not to transmit the PPDU by acquiring a difference(hereinafter, also referred to as an operation offset, an offset, a timedifferent, or an Ack transmission time) between the session start timeand the Ack transmission time through the transmission operationdetermination. For example, in a case where a value of the operationoffset is greater than (or is equal to or greater than) a thresholdconfigured for the wireless communication apparatus 2-1, the wirelesscommunication apparatus 2-1 may determine to transmit the PPDU. In acase where the value of the operation offset is equal to or less than(or is less than) the threshold configured for the wirelesscommunication apparatus 2-1, the wireless communication apparatus 2-1may determine to transmit the PPDU. In a case where the value of theoperation offset is greater than (or is equal to or greater than) thethreshold for the wireless communication apparatus 2-1, the wirelesscommunication apparatus 2-1 may determine not to transmit the PPDU. In acase where the value of the operation offset is equal to or greater than(or is less than) the threshold configured for the wirelesscommunication apparatus 2-1, the wireless communication apparatus 2-1may determine not to transmit the PPDU.

As a method of calculating the value of the operation offset, the valueof the operation offset may be calculated by using operationoffset=session start time−Ack transmission time, operation offset=Acktransmission time−session start time, operation offset=abs (sessionstart time−Ack transmission time), and abs (operation offset=Acktransmission time−session start time). In this method, abs (⋅) may be anoperation for acquiring an absolute value of ⋅.

The wireless communication apparatus 2-1 may determine to transmit thePPDU through the transmission operation determination in a case wherethe PLCP is correctly received, or may determine to transmit the PPDU ina case where the DATA is correctly received. The wireless communicationapparatus 2-1 may determine not to transmit the PPDU through thetransmission operation determination in a case where the PLCP is notable to be correctly received, and may determine not to transmit thePPDU in a case where the DATA is not able to be correctly received.

In a case where the wireless communication apparatus 2-1 determines totransmit the PPDU through the transmission operation determination, thewireless communication apparatus 2-1 may restrict the type (priority,length, frame type (management frame, control frame, or data frame), orframe format) of the PPDU capable of being transmitted by the wirelesscommunication apparatus 2-1. That is, for a period corresponding to theTXTIME or the L-SIG Duration after the reception operation is ended, thewireless communication apparatus 2-1 may specify the type of the PPDUwhich is not capable of being transmitted even though it determined totransmit the PPDU through the transmission operation determination.

For example, the wireless communication apparatus 2-1 may configure suchthat the CF-END frame is not able to be transmitted even though it isdetermined to transmit the PPDU through the transmission operationdetermination.

The wireless communication apparatus 2-1 is able to estimate the sessionend time. For example, the wireless communication apparatus 2-1 maycalculate the session end time by using the Duration informationindicated by the Duration/ID field within the PPDU transmitted by thewireless communication apparatus 1-2. The wireless communicationapparatus 2-1 may use the Duration information as the informationregarding the session end time.

The wireless communication apparatus 2-1 may estimate the session endtime by using the information (also referred to as DATA Duration)regarding the TXTIME, L-SIG Duration, or the LENGTH field. For example,the wireless communication apparatus 2-1 may use a value acquired byadding the information regarding the SIFS period and the BA transmissionperiod to the DATA Duration as the session end time. The wirelesscommunication apparatus 2-1 may use the DATA Duration as the session endtime. The wireless communication apparatus 2-1 may use a value acquiredby adding any one or both of information items regarding IFS and slottime to the DATA Duration as the session end time.

The method of calculating the information regarding the BA transmissionperiod of the wireless communication apparatus 2-1 is not limited. TheBA transmission period may be the transmission period of the PPDUincluding the BA, may be the transmission period of the PPDU includingthe Ack, may be the transmission period of the PPDU including the CTS,or may be the transmission period of the PPDU including the RTS.

The wireless communication apparatus 2-1 may estimate the Acktransmission start time. The Ack transmission start time may beestimated from the DATA Duration or the Duration information.

For example, the wireless communication apparatus 2-1 may estimate thesession end time or the Ack transmission start time from the informationincluded in the PPDU transmitted from the wireless communicationapparatus 1-2, or may estimate the session end time or the Acktransmission start time from the information included in the PPDUtransmitted from the wireless communication apparatus 1-1.

FIG. 12 is a sequence chart showing an example of a flow of theoperation of the wireless communication apparatus 10-1. The wirelesscommunication apparatus 1-2 transmits the PLCP header (step S101 s).Subsequently, the wireless communication apparatus 2-2 receives the PLCPheader, and performs the operation determination for receiving theresult DATA of the reception operation determination (step S102 s).Subsequently, the wireless communication apparatus 1-2 transmits theDATA (step S103 s), and the wireless communication apparatus 2-2receives the DATA (step S104 s). After the reception of the DATA iscompleted, the wireless communication apparatus 2-2 transmits the BAafter the wireless communication apparatus 2-2 is on standby for theSIFS period (step S105 s), and the wireless communication apparatus 1-2receives the BA (step S106 s). The end time of step S105 s or step S106s may be used as the session end time.

Meanwhile, the wireless communication apparatus 2-1 performs thereception operation of the PLCP header, and determines not to performthe reception operation of the DATA subsequent to the PLCP header as theresult of the reception operation (step S107 s). Subsequently, thewireless communication apparatus 1-1 transmits the PLCP header (stepS108 s). Thereafter, the wireless communication apparatus 2-1 receivesthe PLCP header, and performs determination for receiving the DATAsubsequent to the PLCP header as the result of the reception operationdetermination (step S109 s). Subsequently, the wireless communicationapparatus 1-1 transmits the DATA (step S110 s), and the wirelesscommunication apparatus 2-1 receives the DATA (step S111 s). Thewireless communication apparatus 2-1 performs the transmission operationdetermination based on the information regarding the session end timeand the Ack transmission start time. In a case where it is determined totransmit the PPDU, the wireless communication apparatus 2-1 transmitsthe BA after the DATA is received (step S112 s), and the wirelesscommunication apparatus 1-1 receives the BA (step S113 s). The starttime of step S113 s or step S112 s may be the Ack transmission starttime.

According to the apparatuses, the systems, and the methods describedabove, the wireless communication apparatus 2-2 may determine whetherthe wireless communication apparatus that performs the medium protectionoperation or the medium reservation operation is connected to the myBBSor is connected to the OBSS, and may determine whether the wirelesscommunication apparatus 2-2 performs the reception operation or startsthe transmission operation after the medium protection operation or themedium reservation operation based on this determination. By doing this,the restriction of the access of the wireless communication apparatus2-2 to the WM caused by the frame transmission of the wirelesscommunication apparatus which is the exposed terminal is relaxed, andthus, it is possible to improve user throughput.

2. Common to all Embodiments

The programs operated in the wireless communication apparatus 1-1, thewireless communication apparatus 2-1, the wireless communicationapparatus 1-2, and the wireless communication apparatus 2-2 according tothe present invention are programs (programs causing a computer tofunction) that control a CPU such that the functions of the embodimentaccording to the present invention are realized. The information itemstreated by these devices are temporally accumulated in a RAM during theprocessing, are stored in various ROMs or HDDs, are read by the CPU ifneeded, and are modified and rewritten. As a recording medium thatstores the programs, any one of a semiconductor medium (for example, ROMor non-volatile memory card), an optical recording medium (for example,DVD, MO, MD, CD, and BD), a magnetic recording medium (for example,magnetic tape and flexible disk) may be used. The functions of theabove-described embodiment may be realized by executing the loadedprogram, or the functions of the present invention may be realized byprocessing the loaded program in cooperation with an operating system oranother application program based on an instruction of the program.

In a case where the program is distributed to the market, the programmay be distributed while being stored in a portable recording medium,and may be transmitted to a server computer connected via a network suchas the Internet. In this case, a storage device of the server computermay also be included in the present invention. Some or all of thewireless communication apparatus 1-1, the wireless communicationapparatus 2-1, the wireless communication apparatus 1-2, and thewireless communication apparatus 2-2 of the above-described embodimentmay be typically realized as LSI which is integrated circuit. Thefunctional blocks of the wireless communication apparatus 1-1, thewireless communication apparatus 2-1, the wireless communicationapparatus 1-2, and the wireless communication apparatus 2-2 may beseparately realized as chips, or some or all thereof may be integratedand realized as chips. In a case where the functional blocks arerealized as the integrated circuits, an integrated circuit control unitthat controls the integrated circuits is added.

The method of realizing the functional blocks as the integrated circuitis not limited to the LSI, and the functional blocks may be realized bya dedicated circuit or a general-purpose processor. In a case where atechnology of realizing the functional blocks as the integrated circuitreplaced as the LSI appears by the advance of a semiconductortechnology, it may be possible to use an integrated circuit producedusing this technology.

This application invention is not limited to the above-describedembodiment. The wireless communication apparatus 1-1, the wirelesscommunication apparatus 2-1, the wireless communication apparatus 1-2,and the wireless communication apparatus 2-2 according to applicationinvention are not limited to the application to a mobile stationapparatus, and may be applied to stationary or non-movable electronicdevices which are installed indoors or outdoors, such as AV devices,kitchen devices, cleaning and washing machines, air conditioners, officedevices, vending machines, and other home appliances.

Although the embodiment of the invention has been described in detailwith reference to drawings, the specific structure is not limited tothis embodiment, and designs within a scope without departing from thegist of the invention are included in the claims.

INDUSTRIAL APPLICABILITY

The present invention is preferably used in the wireless communicationapparatus, the communication method, and the communication system.

The international patent application claims priority based on JapanesePatent Application No. 2015-114372 filed on Jun. 5, 2015, and the entirecontents of Japanese Patent Application No. 2015-114372 are herebyincorporated by reference.

REFERENCE SIGNS LIST

-   -   1-1, 1-2, 2-1, 2-2 Wireless communication apparatus    -   3-1, 3-2 Management range    -   10001-1 Higher layer unit    -   10002-1 Autonomous distribution control unit    -   10002 a-1 CCA unit    -   10002 b-1 Backoff unit    -   10002 c-1 Transmission determination unit    -   10003-1 Transmission unit    -   10003 a-1 Physical layer frame generation unit    -   10003 b-1 Wireless transmission unit    -   10004-1 Reception unit    -   10004 a-1 Wireless reception unit    -   10004 b-1 Signal demodulation unit    -   10005-1 Antenna unit

1. A wireless communication apparatus capable of transmitting andreceiving a physical layer frame, the apparatus comprising: a receptionunit that receives a frame indicating start of a medium protectionoperation, and acquires, from the frame indicating the start of themedium protection operation, BSS identification information foridentifying a BSS to which a transmission-source wireless communicationapparatus of the frame indicating the start of the medium protectionoperation belongs; and a transmission unit that determines whether ornot to start a transmission operation of a frame addressed to anotherwireless communication apparatus belonging to a BSS to which thewireless communication apparatus belongs based on the BSS identificationinformation.
 2. The wireless communication apparatus according to claim1, wherein the reception unit configures an NAV in a case where the BBSidentification information indicates the BSS to which the wirelesscommunication apparatus belongs.
 3. The wireless communication apparatusaccording to claim 2, wherein the transmission unit determines the startof the transmission operation of the frame addressed to the otherwireless communication apparatus belonging to the BSS to which thewireless communication apparatus belongs in a case where the BSSidentification information included in the frame indicating the start ofthe medium protection operation indicates a BSS other than the BSS towhich the wireless communication apparatus is connected.
 4. The wirelesscommunication apparatus according to claim 2, wherein the transmissionunit configures an NAV different from the NAV in a case where thetransmission-source wireless communication apparatus of the frameindicating the start of the medium protection operation is a wirelesscommunication apparatus connected to a BSS other than the BSS to whichthe wireless communication apparatus is connected.
 5. The wirelesscommunication apparatus according to claim 2, wherein the start of thetransmission operation of the frame addressed to the other wirelesscommunication apparatus is prohibited in a case where the frameaddressed to the other wireless communication apparatus is a frame forrequesting a frame reply and a period during which the frame reply isexpected matches a period during which the transmission-source wirelesscommunication apparatus of the frame indicating the start of the mediumprotection operation performs frame transmission in whole or part withina period during which the medium protection operation is reserved. 6.The wireless communication apparatus according to claim 1, wherein theBSS identification information is a MAC address indicating thetransmission-source wireless communication apparatus of the frameindicating the start of the medium protection operation.
 7. The wirelesscommunication apparatus according to claim 1, wherein the BSSidentification information is BSS color written in a PHY header of theframe indicating the start of the medium protection operation.
 8. Thewireless communication apparatus according to claim 2, wherein the BSSidentification information is information indicating a destinationwireless communication apparatus of the frame indicating the start ofthe medium protection operation, wherein the reception unit retains a TAaddress set which is a set of information items indicatingtransmission-source wireless communication apparatuses of previouslyreceived frames, and wherein the transmission unit starts thetransmission operation of the frame addressed to the other wirelesscommunication apparatus in a case where the information indicating thedestination wireless communication apparatus of the frame indicating thestart of the medium protection operation is not present in the TAaddress set.
 9. A communication method of a wireless communicationapparatus capable of transmitting and receiving a physical layer frame,the method comprising: a step of receiving a frame indicating start of amedium protection operation; a step of acquiring, from the frameindicating the start of the medium protection operation, BSSidentification information for identifying a BSS to which atransmission-source wireless communication apparatus of the frameindicating the start of the medium protection operation belongs; and astep of determining whether or not to start a transmission operation ofa frame addressed to another wireless communication apparatus belongingto a BSS to which the wireless communication apparatus belongs based onthe BSS identification information.
 10. A communication system includinga first wireless communication apparatus and a second wirelesscommunication apparatus which are capable of transmitting and receivinga physical layer frame, the first wireless communication apparatusincluding a transmission unit that transmits a frame, which indicatesstart of a medium protection operation and includes BSS identificationinformation for identifying a BSS to which the first wirelesscommunication apparatus belongs, the second wireless communicationapparatus including a reception unit that receives the frame indicatingstart of the medium protection operation, and acquires the BSSidentification information for identifying the BSS to which the firstwireless communication apparatus belongs from the frame indicating thestart of the medium protection operation, and a transmission unit thatdetermines whether or not to start a transmission operation of a frameaddressed to another wireless communication apparatus belonging to a BSSto which the second wireless communication apparatus belongs based onthe BSS identification information.